linux-kernel - Re: [PATCH v1 09/47] vidoe: fbdev: atyfb: remove and fix MTRR MMIO "hole" work around

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Date:	Fri, 27 Mar 2015 21:12:01 +0100
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Juergen Gross <jgross@...e.com>,
	Jan Beulich <JBeulich@...e.com>, Borislav Petkov <bp@...e.de>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	venkatesh.pallipadi@...el.com, Dave Airlie <airlied@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
	X86 ML <x86@...nel.org>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	Antonino Daplas <adaplas@...il.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>
Subject: Re: [PATCH v1 09/47] vidoe: fbdev: atyfb: remove and fix MTRR MMIO
 "hole" work around

On Fri, Mar 20, 2015 at 04:52:18PM -0700, Andy Lutomirski wrote:
> On Fri, Mar 20, 2015 at 4:17 PM, Luis R. Rodriguez
> <mcgrof@...not-panic.com> wrote:
> > diff --git a/drivers/video/fbdev/aty/atyfb_base.c b/drivers/video/fbdev/aty/atyfb_base.c
> > index 8025624..8875e56 100644
> > --- a/drivers/video/fbdev/aty/atyfb_base.c
> > +++ b/drivers/video/fbdev/aty/atyfb_base.c
> > @@ -2630,21 +2630,10 @@ static int aty_init(struct fb_info *info)
> >
> >  #ifdef CONFIG_MTRR
> >         par->mtrr_aper = -1;
> > -       par->mtrr_reg = -1;
> >         if (!nomtrr) {
> > -               /* Cover the whole resource. */
> > -               par->mtrr_aper = mtrr_add(par->res_start, par->res_size,
> > +               par->mtrr_aper = mtrr_add(info->fix.smem_start,
> > +                                         info->fix.smem_len,
> >                                           MTRR_TYPE_WRCOMB, 1);
> > -               if (par->mtrr_aper >= 0 && !par->aux_start) {
> > -                       /* Make a hole for mmio. */
> > -                       par->mtrr_reg = mtrr_add(par->res_start + 0x800000 -
> > -                                                GUI_RESERVE, GUI_RESERVE,
> > -                                                MTRR_TYPE_UNCACHABLE, 1);
> > -                       if (par->mtrr_reg < 0) {
> > -                               mtrr_del(par->mtrr_aper, 0, 0);
> > -                               par->mtrr_aper = -1;
> > -                       }
> > -               }
> >         }
> >  #endif
> >
> > @@ -2776,10 +2765,6 @@ aty_init_exit:
> >         par->pll_ops->set_pll(info, &par->saved_pll);
> >
> >  #ifdef CONFIG_MTRR
> > -       if (par->mtrr_reg >= 0) {
> > -               mtrr_del(par->mtrr_reg, 0, 0);
> > -               par->mtrr_reg = -1;
> > -       }
> >         if (par->mtrr_aper >= 0) {
> >                 mtrr_del(par->mtrr_aper, 0, 0);
> >                 par->mtrr_aper = -1;
> > @@ -3466,7 +3451,7 @@ static int atyfb_setup_generic(struct pci_dev *pdev, struct fb_info *info,
> >         }
> >
> >         info->fix.mmio_start = raddr;
> > -       par->ati_regbase = ioremap(info->fix.mmio_start, 0x1000);
> > +       par->ati_regbase = ioremap_nocache(info->fix.mmio_start, 0x1000);
> 
> Double-check me, but I think that ioremap_nocache + WC MTRR = WC. 

Precicely, in this case the WC hole was obtained by using MTRR WC. This
patch removes that WC hole trick and now we can be explciit about
only wanting ioremap_nocache() on the registers, that is WC is not
desired here and is not used. The patch does not highlight the fact
that there was left in place another ioremap() call for the framebuffer:

info->screen_base = ioremap(info->fix.smem_start, info->fix.smem_len);

That is the one that later after this patch we use ioremap_wc() for.
This patch just removes the hole solution. That's all.

  Luis
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